The long-term goal of our research is to elucidate the role of microsatellite DNA sequence variation in neoplastic progression. The objective of this proposal is to identify the full complement of biochemical mechanisms that act to stabilize microsatellite sequences in human cells. Our working hypothesis is that cellular microsatellite mutation rates are the cumulative result of proteins acting to maintain genomic stability during DNA replication. We have developed complementary in vitro/ex vivo assays to study mutagenesis within reporter microsatellites in somatic human cells.
Specific Aim 1 will test the hypothesis that DNA polymerase pausing within microsatellite sequences can impede replication fork progression, and that RecQ helicases have a specialized function during microsatellite DNA replication. Biochemical analyses of replication intermediates through microsatellites of differing sequence will be performed using cell lines from normal, Bloom and Werner syndrome donors to the function of BLM and WRN helicases. Mutation rates within the herpes simplex virus thymidine kinase (HSV-tk) gene reporter cassettes will be quantitated to determine whether these helicases function to stabilize microsatellite DNA sequences.
Specific Aim 2 will determine the contribution of enzymatic activities associated with the replication fork in maintaining genome stability. We will test the contribution of mismatch repair proteins to the stability of tetranucleotide alleles and microsatellites with potential secondary structure, and test the contribution of the Mre11/NBS/Rad50 complex to human cell replication fidelity. The ex vivo shuttle vector system will be used in naturally occurring MLH1, PMS2, NBS1 and hMre11-defective lymphoblastoid cell lines, and in cells with gene expression down-regulated by antisense methods. Mutation rates and specificities will be determined to establish whether the activities of NBS and hMre11 affect replication fidelity.
Specific Aim 3 will determine the relative contribution of replicative and Y family DNA polymerases to spontaneous mutagenesis and microsatellite stability. The in vitro HSV-tk assay will be used to analyze DNA polymerase delta and polymerase kappa (pol kappa) error rates at microsatellites. The effects of pol kappa levels on spontaneous cellular mutagenesis will be analyzed using the ex vivo assay cell lines containing either pol kappa overexpression vectors or stable ribozymes to down-regulated pol kappa expression. These studies will establish whether regulation of pol kappa activity is a potential avenue for therapeutic interventions aimed at regulating genome stability. This proposed research has direct implications for modeling tumor progression, as the loss of genomic surveillance mechanisms will accelerate microsatellite mutagenesis. Microsatellite allele lengths can directly affect gene expression. As microsatellites are polymorphic in human populations, this effect on gene regulation may be an important factor contributing to individual cancer risk.

Agency
National Institute of Health (NIH)
Institute
National Cancer Institute (NCI)
Type
Research Project (R01)
Project #
5R01CA100060-05
Application #
7535534
Study Section
Cancer Etiology Study Section (CE)
Program Officer
Okano, Paul
Project Start
2005-01-01
Project End
2010-12-31
Budget Start
2009-01-01
Budget End
2010-12-31
Support Year
5
Fiscal Year
2009
Total Cost
$298,277
Indirect Cost
Name
Pennsylvania State University
Department
Pathology
Type
Schools of Medicine
DUNS #
129348186
City
Hershey
State
PA
Country
United States
Zip Code
17033
Hile, Suzanne E; Shabashev, Samion; Eckert, Kristin A (2013) Tumor-specific microsatellite instability: do distinct mechanisms underlie the MSI-L and EMAST phenotypes? Mutat Res 743-744:67-77
Walsh, Erin; Wang, Xiaoxiao; Lee, Marietta Y et al. (2013) Mechanism of replicative DNA polymerase delta pausing and a potential role for DNA polymerase kappa in common fragile site replication. J Mol Biol 425:232-43
Hile, Suzanne E; Wang, Xiaoxiao; Lee, Marietta Y W T et al. (2012) Beyond translesion synthesis: polymerase ? fidelity as a potential determinant of microsatellite stability. Nucleic Acids Res 40:1636-47
Abdulovic, Amy L; Hile, Suzanne E; Kunkel, Thomas A et al. (2011) The in vitro fidelity of yeast DNA polymerase ? and polymerase ? holoenzymes during dinucleotide microsatellite DNA synthesis. DNA Repair (Amst) 10:497-505
Damerla, Rama Rao; Knickelbein, Kelly E; Kepchia, Devin et al. (2010) Telomeric repeat mutagenicity in human somatic cells is modulated by repeat orientation and G-quadruplex stability. DNA Repair (Amst) 9:1119-29
Shah, Sandeep N; Hile, Suzanne E; Eckert, Kristin A (2010) Defective mismatch repair, microsatellite mutation bias, and variability in clinical cancer phenotypes. Cancer Res 70:431-5
Shah, Sandeep N; Opresko, Patricia L; Meng, Xiao et al. (2010) DNA structure and the Werner protein modulate human DNA polymerase delta-dependent replication dynamics within the common fragile site FRA16D. Nucleic Acids Res 38:1149-62
Kelkar, Yogeshwar D; Strubczewski, Noelle; Hile, Suzanne E et al. (2010) What is a microsatellite: a computational and experimental definition based upon repeat mutational behavior at A/T and GT/AC repeats. Genome Biol Evol 2:620-35
Eckert, Kristin A; Hile, Suzanne E (2009) Every microsatellite is different: Intrinsic DNA features dictate mutagenesis of common microsatellites present in the human genome. Mol Carcinog 48:379-88
Shah, Sandeep N; Eckert, Kristin A (2009) Human postmeiotic segregation 2 exhibits biased repair at tetranucleotide microsatellite sequences. Cancer Res 69:1143-9

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